Becoming a fully functioning social being requires learning the social norms (or rules) that constrain behavior within one's social group, and monitoring the behavior of oneself and others with respect to them. Recent evidence indicates that children as young as three years of age reason as effectively as adults on tasks that require monitoring the behavior of others with respect to prescriptive social rules. Other evidence shows that reference to social rules appear in the justifications given for behavior earlier (within the second year of life), but systematic investigation of social rule reasoning strategies in this age group has been precluded by the language-intensive nature of the tasks. The specific aim of the proposed work is to adapt looking time methodology for use in investigating the social reasoning strategies of children younger than three years of age in order to track the emergence and development of this important type of reasoning skill. Across three experiments, looking time preferences of sixty 18-month-old infants (3 mos) will be investigated in order to assess their understanding of prescriptive social rules. Simple prescriptive rules such as "All the kids have to hold hands" will be accompanied by paired visual displays, one of which depicts compliance with the rule while the other depicts non-compliance. When reasoning about prescriptive rules, older children and adults typically attend to and choose to inspect possible instances of rule-violation. If, like older children and adults, children in this age group understand the social implications of prescriptive rules, they should exhibit a preference for looking at depictions of rule-violations (the depictions that are inconsistent with the rule). To rule out the possibility that these depictions are simply more interesting visually, a control condition will be employed in which the same displays are accompanied by a similarly-worded declarative statement, such as "All the kids are holding hands". If the inconsistent depiction is simply more interesting visually, there should be no difference in looking time preferences between the social and declarative conditions (i.e., infants should look at the inconsistent depiction in both cases). These results, should they obtain, will validate the use of looking time methodology for use in investigating early-emerging social cognition, and for use in identifying impairments in its development in at-risk populations.